Dual mode searchlight dimming controller systems and methods

ABSTRACT

A solid state microprocessor or digital signal processor (DSP) for dual mode illumination and dimming into modern aerospace searchlights. The system is a universal dimming platform with “smart functions” that include and are not limited to multiple light intensity linearization curves, analog and/or digital input dimming interface, built-in tests and health monitoring, synchronized dual mode light output with canopy position, light driver redundancy, lamp life reporting, and controlled switching with improved EMI. With real-time monitoring of the system parameters it monitors the lights proper operation and failures which can be a concern for flight-critical lighting.

PRIORITY CLAIM

This application claims priority to provisional patent application Ser.No. 60/941,583 filed on Jun. 1, 2007 and is incorporated herein byreference.

GOVERNMENT RIGHTS

The U.S. Government may have rights to this invention under U.S. Armycontract number DAAH23-03-D-0204.

BACKGROUND OF THE INVENTION

Aerospace searchlights that are based on mechanical switches or relayshave limited or no built-in capabilities for visible (VIS) or infrared(IR) light dimming. In such searchlights the added dimming functionalityin most cases will require two external dimmers; one for the VIS and theother for the IR. Because light dimming requires added electroniccomponents within a limited space, and because of the added challengesin thermal management and electromagnetic interference (EMI), recentsolid state based dual mode searchlights controllers are limited tomotor actuation control and light source enabling or disabling withoutdimming. Older searchlight technologies do not support programmable dualmode universal light controls, interface to the canopy position, orintegration to aircraft management systems.

SUMMARY OF THE INVENTION

The present invention provides a solid state microprocessor or digitalsignal processor (DSP) (a system controller) for dual mode illuminationand dimming into modern aerospace searchlights. The present inventionprovides a universal dimming platform with “smart functions” thatinclude and are not limited to multiple light intensity linearizationcurves, analog and/or digital input dimming interfaces, built-in testsand health monitoring, synchronized dual mode light output with canopyposition, light driver redundancy, lamp life reporting, and controlledswitching with improved EMI. With real-time monitoring of thesearchlight parameters, the system controller monitors the lights properoperation and failures which can be a concern for flight-criticallighting.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred and alternative embodiments of the present invention aredescribed in detail below with reference to the following drawings:

FIGS. 1-3 are schematic diagrams of an example system formed inaccordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, a microprocessor or digital signal processor(DSP)-based dimming control system 20 provides a universal programmableplatform that can be modified to meet the needs of various lightingsystems requiring variable light intensity. In one embodiment, thesystem 20 provides two modes of illumination. The first mode is visiblelight illumination, based on halogen or incandescent lighting, and thesecond mode of illumination is infrared (IR) illumination, based onsolid state light-emitting diodes (LED). The system 20 provides dimmingcontrol during the two modes of illumination. The system 20 performsself adjustment in order to provide linear dimming from 0-100%intensity.

In one embodiment, the system 20 includes a controller 24, a visiblelight circuit 28, an IR light circuit 30, memory 34, a canopy system 36,user interface controls 32, and one or more environmental sensors 40.The controller 24 receives information from the user interface controls32, the canopy system 36, stored data from memory 34 and environmentsensor data in order to determine how to control operation of thecircuits 28, 30. The controller 24 may be an off-the-shelfmicroprocessor or DSP that is programmed to operate as described below.

The circuits 28, 30 include visible and IR lights that are part of asearchlight included on a rotating hub that is housed in a canopy. Thecanopy system 36 provides enable and disable signals based on canopyfeedback sensor(s) (not shown) to the controller 24. When the feedbacksensor(s) determines when the searchlight is clear of a aircraftmounting platform (not shown), an enable signal is produced. Thecontroller 24 controls operation of the circuits 28, 30 based on thereceived enable and disable signals. In one embodiment, the controller24 and canopy system 36 communicate using a serial communicationinterface or other comparable communication signaling method.

In one embodiment, the controller 24 operates in a relativelyhigh-voltage state thereby reducing the noise-to-signal ratio as much aspossible. For example, signals outputted by the controller 24 are levelshifted from 3.3 VDC to 5.0 VDC (see level shifts in the followingfigures). Similarly, input signals to the controller 24 are shifted downfrom 5.0 VDC to 3.3 VDC. Also, communication with the nonvolatile memory34 is performed using a serial or other type of digital interface. Thecontroller frequency is set by a built-in phase locked loop (PLL) andthe base frequency is set by an external crystal oscillator.

The memory 34 may include electrically erasable, programmable, read-onlymemory (EEPROM) or flash memory that is in communication with thecontroller 24. The controller 24 may include various other types ofwired or wireless communication means, such as a joint test action group(JTAG) interface or RS-232 that allow connection of an externaldiagnostic system (not shown), such as a hand-held computer system.

In one embodiment, the environmental sensors 40 include a temperaturesensor (not shown) that is mounted within or near the circuit 28, 30.The temperature sensor outputs a temperature signal to the controller24. The controller 24 analyzes the received temperature signal todetermine if the sensed temperature is above a predefined thresholdtemperature limit. If the sensed temperature is above the thresholdtemperature limit, then the controller 24 records a fault into thememory 34 and may deactivate the respective circuit 28, 30.

FIG. 2 illustrates a more detailed example of the visible light circuit28. The circuit 28 includes level shifts 70, 74, a driver isolation(charge pump) component 72, four switches 54, 56, 66, 68, two halogen orincandescent lights 60, 62, two current sensors 78, 80, and twoamplifier filters 82, 84. The level shifts 70, 74 are configured toreceive two pulse-width modulation (PWM) independent control signalsfrom the controller 24. In one embodiment, the switches 54, 56, 66, 68are N-channel MOSFETs. The drains of switches 54, 56 are connected to amain bus power supply 50. The main bus power supply 50 supplies a sourcevoltage, an average voltage value and a current value to the controller24 for analysis. The source of the switch 54 is connected to a firstlead of the light 60. The source of the switch 56 is connected to asecond lead of the light 60 and a first lead of the light 62. The gateof the switch 54 is connected to the driver isolation component 72 inorder to receive an adjusted PWM1 signal from the controller 24. Thegate of the switch 56 is connected to the driver isolation component 72in order to receive an adjusted PWM2 signal. PWM1 and PWM2 are increasedin voltage by the level shift 70 and are controlled by the driverisolation component 72 in order to maintain the switches 54, 56 withinan operating zone, because their sources are not connected to ground.The second level shift 74 receives a PWM3 signal and PWM4 signal fromthe controller 24. The PWM3 signal is increased in voltage by the levelshift 74 and sent to the gate of the switch 66. The drain of the switch66 is connected to a second lead of the light 62. The source of theswitch 66 is connected to ground through the first current sensor 78.The PWM4 signal is increased in voltage by the level shift 74 and sentto the gate of the switch 68. The drain of the switch 68 is connected tothe second lead of the light 60 and the first lead of the light 62. Thesource of the switch 68 is connected to ground through the secondcurrent sensor 80. The current sensors 78, 80 are connected torespective amplification filters 82, 84, which block high frequencynoises and increase the resolution with a higher signal-to-noise ratio.The output of the amplification filters 82, 84 are sent to thecontroller 24 via analog to digital (A/D) converters 87, 88.

The PWM1-4 signals (channels) are independent with adjustable frequencyin phase in order to reduce electromagnetic interference (EMI). ThePWM1-4 signals control the voltage modulation across the switches 54,56, 66, 68 and thus the power across the two lights 60, 62. After theenable signal is received from the canopy system 36 and a visible lampON/OFF switch has been activated in the ON position (and possibly amaster light ON signal), the PWM1 and PWM3 signals activate theirswitches 54, 66, while the PWM2 and PWM4 signals do not. This causespower supplied by the main bus power supply 50 to pass through theswitch 54 through the lights 60, 62 and then to ground through theswitch 66 and current sensor 78. The controller 24 performs dimmingafter a dimming signal has been received from the user interfacecontrols 32. Dimming of the halogen or incandescent lights 60, 62 isperformed by changing the duty cycle of PWM1 and PWM3 signals. Thecontroller 24 determines the duty cycle according to information storedin the memory 34. The stored information includes a brightnesslinearization curve and a PWM duty cycle for a desired light output.

During a running condition and after a specific halogen or incandescentstart-up delay, the average halogen or incandescent current is monitoredby the controller 24 to determine whether the lamp current outputted bythe analog to digital (A/D) converter 87 is above the normal operatinglevel. If the current exceeds the normal level, the halogen orincandescent lights 60, 62 may be deactivated for a specific predefinedperiod of time followed by a restart attempt provided that the halogenor incandescent command is still being issued. The controller 24identifies this condition as a fault and records the fault in the memory34. If the controller 24 determines that this improper lamp currentstill exists, the lights 60, 62 may be shut down. In one embodiment, thefunctionality provided by the A/D converter 86 can be performed by otherdevices, such as an external hardware interrupt request (IRQ), whichforces the DSP (controller 24) to stop the execution and support ofother functions and immediately service the fault related tasks.

The control system 20 provides a “reversionary” mode where the status ofboth light filaments 60 and 62 is continuously monitored and the currentpath is switched to go through the “healthy filament” and bypass thefailed or open filament. The circuit 28 includes an A/D converter 86that samples the voltage between the two lights 60, 62. The A/Dconverter 86 converts the voltage signal to digital form and sends it tothe controller 24 for analysis. If the controller 24 determines that thesample voltage falls below a predefined set value stored in the memory34, an open circuit condition is identified thereby producing anindication that light 60 is in an open state. If this situation occurs,the controller 24 disables the PWM1 signal and enables the PWM2 and PWM3signals, thereby opening the switch 54 and closing the switch 56.

As an alternative “reversionary” and detection method during normaloperation with the switches 54 and 66 are enabled to monitor the currentfrom the sensor 78 and continuously provide its value to the controller24 via the amp filter 82. The controller 24 can change the operation ofthe switches 54, 56, 66, and 68 based on the information received fromthe current sensor 78. For example, if the current sensor 78 shows thatthe current has dropped below a predefined set value, the controller 24disables the switches 56 and 66, and enables the switches 54 and 68,then checks the current sensed at the current sensor 80 as sent throughthe amp filter 84. If the current received from the current sensor 80 isbelow an acceptable value, then the light 60 is in an open state and thelight 62 is still acceptable for use. In this case, the switches 54 and68 will be disabled and the switches 56 and 66 will be enabled. However,if the current sensed at the current sensor 80 is also below thepredefined value, then both of the lights 60, 62 must be replaced.

The controller 24 also monitors voltage and current values from the mainbus power supply 50. If the controller 24 determines that the voltage ofthe main bus power supply 50 exceeds an upper threshold voltage, a faultis logged into the memory 34 and may shut down the lights 60, 62. If thecontroller 24 senses that the voltage has fallen back below the upperthreshold voltage then the controller 24 reactivates the lights 60, 62.

The controller 24 also monitors average voltage produced by the main buspower supply 50. The controller 24 may record average voltage at varioussample rates into the memory 34 and/or may only record when the averagevoltage exceeds a predefined threshold value. The recorded averagevoltage information is used later by a health monitorcomponent/diagnostic system to determine the life of the circuitcomponents, specifically the halogen or incandescent lights 60, 62 andany LEDs. If this condition is detected as a result of the main powerinterruption or simply by shutting off the main power to the lightsystem, the controller 24 will disable the power stage components (54,56, 66, 68, 70, 72, 74, 92, 96, 100, 102, 114, 118, 120, and 122), shutoff the lights 60, 62 and save the latest system variables into thememory 34 until the monitored bus voltage returns to an acceptablevoltage. The last stored variables (parameters or states like faults,temperature, average voltage, . . . etc.) will be the default startingvalues after power interruption recovery.

The controller 24 also receives a current signal from the main bus powersupply 50 for monitoring if the main bus produces an excessive currentspike for a value greater than a predefined threshold stored in memory34. If a current spike greater than the threshold is detected, thecontroller 24 disables power, shuts off the lights 60, 62 and saves thelatest system variables into the memory 34 until the monitored buscurrent returns to a value below the threshold.

FIG. 3 illustrates a more detailed example of the IR light circuit 30from FIG. 1. In one embodiment, the IR light circuit 30 includes aprimary LED circuit 90 and a secondary LED circuit 110. Each of thecircuits 90, 110 are similar. The circuits 90, 110 include a firstswitch 92, 114 (N-channel MOSFET), that receives a supply voltage from avoltage regulator bus 150 that converts the main DC supply voltage intoan appropriate level to operate the LEDs. It also includes a circuit tolimit and regulate the current output. A gate of the switches 92, 114 isconnected to respective power driver EMI filters 100, 120. The source ofthe switches 92, 114 is connected to an input of an LED 94, 116. Theoutputs of the LEDs 94, 116 are connected to a drain of a switch 96, 118(N-channel MOSFET). The gates of the switches 96, 118 are controlled bythe respective power driver EMI filter 100, 120. The sources of theswitches 96, 118 are connected to a current sensor 104, 124. Thecircuits 90, 110 also include level shifts 102, 122 that boosts thevoltage of the received PWM5-8 signals. PWM5-8 signals control operationof the switches 92, 96, 114, 118. During normal operation, the PWM5, 6signals sent to the level shift 102 activate the switches 92 and 96,thereby causing the LED 94 to illuminate. The PWM7, 8 signals deactivatethe switches 114, 118.

The controller 24 minimizes EMI emissions by providing a gradualincrease in the duty cycle of PWM5, 6 and PWM7, 8 signals. Theimplementation of the phase shift between the signals is performed usinghardware and/or software. The controller 24 may include an additionalexternal shift register or delay circuit in order to accomplish thephase shift.

Amplification filters 106, 126 are connected to the current sensors 104,124 for amplifying a current value that is generated by the currentsensors 104, 124. A/D converters 108, 128 convert the output of theamplification filters 106, 126 into digital signals for use by thecontroller 24. The controller 24 determines if an open or short circuitis present based on the signals sent from the current sensors 104, 124via the amplification filters 106, 126 and the A/D converters 108, 128.The controller 24 activates the secondary circuit 110 if the controller24 determines that a short circuit condition exists in the primarycircuit 90. The controller 24 also senses if the LED circuits 90, 110are operating above or below normal operating levels based on the sensedcurrent received from the A/D converters 108, 128. During a runningcondition, and after a specified start-up delay, the controller 24monitors the average sensed current to determine whether the LED 94 or116 is above or below normal operating level. If the current exceeds thenormal level, the controller 24 deactivates the LEDs 94, 116 for aspecified wait period followed by an attempt to restart provided theuser interface controls 32 has IR illumination selected. The controller24 records a fault into the memory 34. If the controller 24 stillidentifies an unacceptable sensed current after the respective circuit90, 110 is restarted, the LEDs 94, 116 are deactivated.

PWM channels 5-8 signals also control the voltage modulation and thuspower across the LEDs 94, 116. The controller 24 provides dimming of theLEDs 94, 116 from light intensities ranging from 0-100% by changing theduty cycle of the respective PWM5-8 signals.

In one embodiment, the system 20 is configured to have default initialfactory dimming levels for the visible light circuit 28 and the IR lightcircuit 30. The factory dimming levels may be stored in the memory 34.If the dimming levels are changed either by an operator or automaticallyby the controller 24, the controller 24 stores the new dimming level inthe memory 34 and uses that as the default illumination condition forthe next activation of the respective circuit.

The PWM1-8 signals are at least partially independent of each other andinclude adjustable frequencies and phases that are controlled by thecontroller 24. This allows the controller 24 to control noise as well asreduce EMI.

The user interface controls 32 include any of a number of or combinationof different types of light and dimming controllers. For example, theuser interface controls 32 include push-button dimming controls oranalog dimming control inputs (0.2-4.8 VDC). Also, the user interfacecontrols 32 include a master lamp ON/OFF momentary switch that activatesall lamp control operations. The activation logic for the master lampswitch is either performed on edge or level logic. A level logic is aconstant voltage level applied (for example 28 VDC or 5 VDC can bedefined as logic high and zero as logic low). If rising or falling edgelogic is used, the edge of switch activation is detected once (logiclow-to-high or high-to-low). When a second edge is detected all lightcontrols are disabled. The enabling and disabling function continues atevery other edge. If a level logic is selected, a logic high enables thelight functions.

The controls 32 also include two independent up/down (brighter anddimmer) momentary switches for controlling dimming of the visible lightcircuit 28 or the IR circuit 30. When one of the dimming controlswitches is activated and held, the controller 24 increases or decreasesthe illumination of the lights 60, 62 or LEDs 94, 116 linearly from0-100% within a period controlled by a variable stored in the memory 34.This variable controls the brightness level as a function of time.

The controller 24 includes a means for adjusting dimming characteristiccurves for the visible light circuit 28 and the IR circuit 30. In oneembodiment, initial implementation may be non-linear. Once the propercharacterization curve has been determined, scaling factors based on acorrelation table/curve or function are applied to linearly dim thelights 60, 62 or LEDs 94, 116. Light photometrics testing is initiallyconducted in the lab (prior to production) to establish the propercorrelation between light output and the PWM duty cycles when dimming isactivated.

Whenever the main power bus (e.g., 28 VDC bus) is recycled (turned OFFand ON), the controller 24 assumes that the lights 60, 62 and LEDs 94,116 are operating properly and operates according to that assumption.

The controller 24 performs a soft start function. When either of thecircuits 28, 30 are activated, the controller 24 ramps up the modulatedduty cycle to a target duty cycle at a predefined rate (stored in memory34).

The controller 24 continuously performs health monitoring analysis. Testmode (for maintenance and diagnostics), fault isolation and life/elapsedrun times for the lights 60, 62 and LEDs 94, 116 are captured and storedin the memory 34 for later diagnostic analysis and system life tracking.The controller 24 detects all faults and stores them in the memory 34,even if the fault condition disappears. Resetting and clearing ofselected fault codes may be manually or automatically performed. Thefollowing is an example of recorded faults from lowest to highest:

1. No fault conditions;

2. Lamp invalid switch command;

3. Lamp bus under-voltage or power off;

4. Lamp power stage over temperature;

5. Lamp bus over-voltage;

6. Secondary LED open circuit;

7. Secondary LED short circuit;

8. Primary LED open circuit;

9. Primary LED short circuit;

10. Halogen or incandescent light open circuit; and

11. Halogen or incandescent short circuit.

The controller 24 can also determine if faulty command control inputsare applied. In such a case, the controller 24 records faulty controlinputs in the memory 34.

While the preferred embodiment of the invention has been illustrated anddescribed, as noted above, many changes can be made without departingfrom the spirit and scope of the invention. Accordingly, the scope ofthe invention is not limited by the disclosure of the preferredembodiment. Instead, the invention should be determined entirely byreference to the claims that follow.

1. A dual mode lighting system comprising: a controller; a visible lightcircuit in signal communication with the controller, the visible lightcircuit comprises: a first light and a second light, the first light andthe second light are at least one of halogen or incandescent lights; afirst switch connected between a power source and a first light; asecond switch connected between the power source and a connectionbetween the first and second lights; a third switch connected betweenthe first and second light and ground; and a fourth switch connectedbetween the second light and ground; an infrared (IR) light circuit insignal communication with the controller; and a user interface in signalcommunication with the controller, wherein the controller controlsoperation of the switches using a plurality of control signals, whereinthe controller controls operation of the circuits based on signalsreceived from the user interface.
 2. The system of claim 1, furthercomprising: a canopy system configured to generate a signal based on thesensed position of the canopy, wherein the controller further controlsoperation of the circuits based on the generated signal.
 3. The systemof claim 1, further comprising: one or more temperature sensorsconfigured to sense temperature proximate to at least one of the lightsor the LEDs and send the sensed temperature to the controller, whereinthe controller further controls operation of the circuits based on thesensed temperature.
 4. The system of claim 1, wherein the switches arefield effect transistors.
 5. The system of claim 4, further comprisingcurrent sensors for sensing current passing though the lights.
 6. Thesystem of claim 5, further comprising a voltage sensor for sensing avoltage supplied by the power source.
 7. The system of claim 6, whereinthe control signals are pulse-width modulation (PWM) signals.
 8. Thesystem of claim 7, wherein the controller dims the lights by controllingduty cycle of the PWM signals based on dimming control signals receivedfrom the user interface, the voltage sensor and the current sensor. 9.The system of claim 7, wherein the IR circuit comprises a primary LEDcircuit and a secondary LED circuit, each of the primary and secondaryLED circuits comprising: a first transistor switch connected to thepower source; an LED with an input connected to the respective firstswitch; and a second transistor switch connected between an output ofthe respective LED and electrical ground.
 10. The system of claim 9,wherein the controller supplies PWM signals to the switches of theprimary and secondary LED circuits based on information received fromthe user interface.
 11. The system of claim 10, wherein the controllerdims either of the LEDs by controlling duty cycle of the PWM signalssent to the switches of the primary and secondary LED circuits based ondimming control signals received from the user interface.
 12. The systemof claim 11, wherein the user interface includes a single device forgenerating the dimming control signals.
 13. The system of claim 10,wherein each of the primary and secondary LED circuits comprise acurrent sensor for detecting current passing through the LED, whereinthe controller further controls operation of the primary and secondarycircuits based on the sensed currents.